Field of the Invention
The present invention relates to a solid-state imaging device capable of suppressing blooming and a control system. Particularly, the present invention relates to a solid-state imaging device such as a CMOS sensor that includes pixels each having a charge converting portion for converting a charge generated by photoelectric conversion into a pixel signal. The term “CMOS image sensor” used herein refers to as an image sensor produced by the application of or partially using the CMOS process. The solid-state imaging device may be formed of a single chip or a plurality of chips.
Description of the Related Art
CMOS image sensors and CCD image sensors have been known as solid-state imaging devices. Blooming has been a typical problem upon producing solid-state imaging devices. Blooming should be suppressed in solid-state imaging devices due to the reason of causing color mixture and color blur. In the case of a CMOS sensor, an overflowed charge leaks into an adjacent pixel to cause blooming and in the case of a CCD sensor, an overflowed charge flows from a photodiode that is a photoelectric converting portion into a vertical transfer register to cause vertical ghost lines.
In particular, when a difference between a bright portion and a dark portion is large in an image such as a starlit sky image captured with a night scene mode (subject including a bright spot in the darkness) or when a difference between a bright portion and a dark portion is large in an image including, for example, a dark spot in the bright portion with high intensity of light, such images may be unclear. Hence blooming should be suppressed.
In order to suppress blooming caused when an amount of charge is saturated (Qssat), there is typically proposed a method of changing a charge accumulation time in response to an amount of received light. In addition, there is known a method of changing an overflow potential barrier (hereinafter referred to as an “overflow barrier”) by controlling a substrate voltage. In the case where such overflow barrier is changed, there are two kinds of methods employed for accumulating more charges, that is, raising an amount of charge saturated (Qssat). Japanese Unexamined Patent Application Publication No. 2003-153084 and Japanese Unexamined Patent Application Publication No. 9-139486 disclose a method of lowering a substrate power supply (voltage) to raise an overflow barrier. With another method, the substrate power supply (voltage) is increased by reducing an overflow barrier in the depth direction of the substrate so that redundant charges be discharged to the substrate.
A method of suppressing blooming by controlling a substrate voltage is proposed for CCD sensors. CCD sensors use a high power supply voltage (not less than 10V), and hence the method of lowering a substrate power supply voltage to raise an overflow barrier is efficient.
On the other hand, for CMOS sensors, there is proposed a method of suppressing blooming by controlling impurities of a semiconductor well region (i.e., sensor well region) formed on a semiconductor substrate while a substrate voltage is constant to set an overflow barrier.